Method and system for upgrading biogas

ABSTRACT

A method for providing renewable natural gas (RNG) includes removing hydrogen sulfide and/or carbon dioxide from biogas to provide partially purified biogas, which may be stored in a mobile storage tank. The partially purified biogas is transported to a biogas upgrading facility, at least partially by truck, rail, or ship. At the biogas upgrading facility, the partially purified biogas is further purified to provide the RNG, which can be injected into a distribution system (e.g., natural gas grid) and/or provided for use in transportation.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application claims benefit of U.S. Provisional Application No.62/696,006 filed Jul. 10, 2018, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a method and system for upgradingbiogas, and in particular, relates to a method and system for upgradingbiogas to renewable natural gas (RNG) that includes the partialpurification of the biogas followed by transport.

BACKGROUND

Biogas, which is a mixture of several gases, is typically produced bythe breakdown of organic matter in low oxygen conditions. In particular,it may be produced by the anaerobic digestion or fermentation of organicmatter (e.g., manure, sewage sludge, municipal solid waste,biodegradable waste, biodegradable feedstock. etc.).

Biogas collected at its source (e.g., a landfill or anaerobic digester)may be referred to as raw biogas. The composition of raw biogas, whichmay vary with the type of organic matter from which it is derived, ispredominately methane (CH₄) and carbon dioxide (CO₂), with small and/ornegligible amounts of nitrogen (N₂), hydrogen sulfide (H₂S), water(H₂O), ammonia (NH₃), hydrogen (H₂), carbon monoxide (CO), oxygen (O₂),volatile organic compounds (VOCs), and/or siloxanes. For example,without being limiting, the composition of raw biogas may include about60% CH₄ (e.g., between about 35% and about 75%), about 35% CO₂ (e.g.,between about 15% and about 65%), about 0-20% N₂, and about 0-5% O₂.

While raw biogas may have sufficient energy content to be combusted(e.g., in an engine, turbine, or boiler) without removing inertcomponents such as CO₂ and/or N₂, another option is to upgrade the rawbiogas for injection into a natural gas distribution system. Biogasupgrading refers to a process that increases the calorific value ofbiogas by removing at least CO₂ and/or N₂, and typically some othercontaminants, thereby increasing the relative amount of CH₄. When rawbiogas is upgraded to the extent that it meets applicable specificationsof the natural gas distribution system (e.g., pipeline standards) and/oris suitable for use in the transportation sector, it is referred to as“renewable natural gas.” Renewable natural gas (RNG) is substantiallyinterchangeable with natural gas and thus can be used as a substitutefor fossil natural gas, can be injected into the natural gasdistribution system, and/or can be used as a transportation fuel whereit can qualify for fuel credits.

In general, when raw biogas is upgraded to RNG, the biogas upgrading isassociated with relatively high capital investment costs, and as aresult, is not generally economically feasible for biogas producershaving a low volume production (e.g., small farms, small landfills, orsmall wastewater treatment facilities).

SUMMARY

The present disclosure describes an improved method and/or system forupgrading biogas wherein raw biogas is partially purified (e.g., at apre-processing site near the source of raw biogas) prior to beingtransported to a centralized biogas upgrading facility where thepartially purified biogas is further purified to renewable natural gas(RNG). The RNG can be injected into a natural gas distribution system,or can be used to provide compressed natural gas (bio-CNG) or liquefiednatural gas (bio-LNG) to an off-grid industrial site or filling station(e.g., a commercial fuel station).

Advantageously, since the centralized biogas upgrading facility canreceive biogas from a plurality of sources (e.g., a plurality ofpre-processing sites and/or raw biogas from one or more other sources),the biogas upgrading can profit from the economies of scale.

Further advantageously, since the partial purification can be conductedprior to transport to the centralized biogas upgrading facility, theprocess/system is more efficient. For example, when the partialpurification includes removing contaminates such as H₂O and H₂S, thiscan reduce corrosion problems and/or safety issues. When the partialpurification includes removing CO₂, this can improve the compressionprocess and/or allow more methane to be transported per unit of volumeat a given pressure, and thus reduce costs.

In accordance with one aspect of the instant invention there is provideda method comprising: a) obtaining biogas from a plurality of biogassources, including a first biogas from a first biogas source and asecond other biogas from a second other biogas source; b) removing oneor more components from the first biogas to produce a first partiallypurified biogas, said one or more components comprising hydrogensulfide, carbon dioxide, or a combination thereof, said one or morecomponents removed using at least one stationary purification system; c)transporting a first vessel containing the first partially purifiedbiogas to a biogas upgrading facility; d) removing one or morecomponents from the second biogas to produce a second partially purifiedbiogas, said one or more components comprising hydrogen sulfide, carbondioxide, or a combination thereof, said one or more components removedusing at least one stationary purification system; e) optionally,transporting a second vessel containing the second partially purifiedbiogas to the biogas upgrading facility; f) at the biogas upgradingfacility, removing at least one component from a gas stream comprisingthe first partially purified biogas, the second partially purifiedbiogas, or a combination thereof, to produce renewable natural gashaving a heating value that is greater than a heating value of any oneof the first and second partially purified biogases; g) providing therenewable natural gas produced in f) for injection into a distributionsystem, for use as a transportation fuel, or for a combination thereof.

In accordance with one aspect of the instant invention there is provideda method comprising: a) obtaining biogas from a plurality of biogassources, including a first biogas from a first biogas source and asecond other biogas from a second other biogas source; b) feeding thefirst biogas into a first stationary purification system to removehydrogen sulfide, carbon dioxide, or a combination thereof from thefirst biogas and produce a first partially purified biogas having aheating value less than 950 BTU/scf; c) transporting a first vesselcontaining the first partially purified biogas to a biogas upgradingfacility by vehicle; d) feeding the second biogas into a second otherstationary purification system to remove hydrogen sulfide, carbondioxide, or a combination thereof from the second biogas and produce asecond partially purified biogas having a heating value less than 950BTU/scf; e) optionally, transporting a second vessel containing thesecond partially purified biogas to the biogas upgrading facility byvehicle; f) at the biogas upgrading facility, feeding the first andsecond partially purified biogases into one or more purification systemsto remove carbon dioxide, nitrogen, oxygen, or any combination thereofand to produce renewable natural gas having a heating value that is atleast 950 BTU/scf; and g) providing renewable natural gas produced in f)for injection into a distribution system, for use as a transportationfuel, or for a combination thereof.

In accordance with one aspect of the instant invention there is provideda method for upgrading biogas comprising: (a) obtaining biogas from abiogas source; (b) producing partially purified biogas from the biogas,said producing comprising removing hydrogen sulfide, carbon dioxide, ora combination thereof from the biogas using at least one stationarypurification system; (c) filling a vessel with the partially purifiedbiogas; (d) transporting the vessel containing the partially purifiedbiogas to a destination; (e) at the destination, removing the partiallypurified biogas produced from the vessel; (f) purifying a gas streamcomprising partially purified biogas removed from the vessel to producerenewable natural gas; and (g) providing the renewable natural gas forinjection into a natural gas distribution system, use as atransportation fuel, or a combination thereof.

In accordance with one aspect of the instant invention there is provideda method of upgrading biogas comprising: obtaining partially purifiedbiogas from a plurality of pre-processing sites, each pre-processingsite including a source of biogas, a stationary purification system forproducing the partially purified biogas, and a vessel for storing thepartially purified biogas at a pressure of at least 1000 psig;transporting each vessel containing partially purified biogas directlyto a biogas upgrading facility; removing the partially purified biogasfrom each vessel at the biogas upgrading facility; further purifying thepartially purified biogas removed from each vessel to provide renewablenatural gas, where the renewable natural gas has a heating value of atleast 950 BTU/scf and is for injection into a distribution system, foruse as a transportation fuel, or a combination thereof.

In accordance with one aspect of the instant invention there is provideda method for upgrading biogas comprising: at a first location, providinga first stationary biogas purification system for processing biogas froma first biogas source; at a second location, providing a second otherstationary biogas purification system for processing biogas from asecond other biogas source; collecting or arranging for the collectionof partially purified biogas produced at each of the first and secondlocations, said collecting comprising coupling a vessel or a containersupporting the vessel to a truck, rail car, or ship, and transportingthe vessel, where the vessel contains partially purified biogas producedat the first or second location; and producing renewable natural gasfrom the transported partially purified biogas, said producingcomprising removing carbon dioxide, nitrogen, oxygen, or any combinationthereof, from the transported partially purified biogas.

In accordance with one aspect of the instant invention there is provideda method of upgrading biogas comprising: at a pre-processing site,removing water, hydrogen sulfide, carbon dioxide, or any combinationthereof from raw biogas to produce partially purified biogas,compressing the partially purified biogas, and feeding the compressedpartially purified biogas to a vessel as it is produced, said vesseldecoupled from a vehicle; transporting the partially purified biogas toa biogas upgrading facility, said transporting comprising moving saidvessel by vehicle; at the biogas upgrading facility, decoupling thevessel from the vehicle and removing the partially purified biogastherefrom; further purifying the partially purified biogas removed toproduce renewable natural gas; and providing the renewable natural gasfor injection into a natural gas distribution system, for use as atransportation fuel, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a method according to one embodiment of theinvention;

FIG. 2 is a flow diagram of a method according to one embodiment of theinvention;

FIG. 3a is a schematic diagram showing a system for providing RNG inaccordance with an embodiment of the invention;

FIG. 3b is a schematic diagram showing a system for providing RNG inaccordance with another embodiment of the invention;

FIG. 3c is a schematic diagram showing a system for providing RNG inaccordance with another embodiment of the invention; and

FIG. 3d is a schematic diagram showing a system for providing RNG inaccordance with another embodiment of the invention.

DETAILED DESCRIPTION

Certain exemplary embodiments of the invention now will be described inmore detail, with reference to the drawings, in which like features areidentified by like reference numerals. The invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. The terminology used herein is forthe purpose of describing certain embodiments only and is not intendedto be limiting of the invention. For example, as used herein, thesingular forms “a,” “an,” and “the” may include plural references unlessthe context clearly dictates otherwise. The terms “comprises”,“comprising”, “including”, and/or “includes”, as used herein, areintended to mean “including but not limited to.” The term “and/or”, asused herein, is intended to refer to either or both of the elements soconjoined. The phrase “at least one” in reference to a list of one ormore elements, is intended to refer to at least one element selectedfrom any one or more of the elements in the list of elements, but notnecessarily including at least one of each and every elementspecifically listed within the list of elements. Thus, as a non-limitingexample, the phrase “at least one of A and B” may refer to at least oneA with no B present, at least one B with no A present, or at least one Aand at least one B in combination. In the context of describing thecombining of components by the “addition” or “adding” of one componentto another, or the separating of components by the “removal” or“removing” of one component from another, those skilled in the art willunderstand that the order of addition/removal is not critical (unlessstated otherwise). The terms “remove”, “removing”, and “removal”, withreference to one or more impurities, contaminants, and/or constituentsof biogas, includes partial removal. The terms “cause” or “causing”, asused herein, may include arranging or bringing about a specific result(e.g., a withdrawal of a gas), either directly or indirectly, or to playa role in a series of activities through commercial arrangements such asa written agreement, verbal agreement, or contract. The term “associatedwith”, as used herein with reference to two elements (e.g., a fuelcredit associated with the transportation fuel), is intended to refer tothe two elements being connected with each other, linked to each other,related in some way, dependent upon each other in some way, and/or insome relationship with each other. The terms “first”, “second”, etc.,may be used to distinguish one element from another, and these elementsshould not be limited by these terms. The term “plurality”, as usedherein, refers to two or more. Unless defined otherwise, all technicaland scientific terms used herein have the same meanings as commonlyunderstood by one of ordinary skill in the art.

Referring to FIG. 1, there is shown a method in accordance with oneembodiment of the invention. In 10, raw biogas is obtained (e.g.,withdrawn from the source). In 20, the raw biogas, which contains bothCH₄ and CO₂, is subject to a partial purification process (e.g., thatremoves at least one of H₂O, H₂S, and CO₂) to produce partially purifiedbiogas. In 40, the resulting partially purified biogas is collectedand/or transported (e.g., by truck, rail, or ship). In 50, the partiallypurified biogas is further purified to produce RNG. The RNG is providedto a user 60 and/or distribution system.

The term “biogas”, as used herein, refers to a gas mixture that containsmethane produced from the anaerobic digestion of organic matter. Rawbiogas refers to biogas before it is treated to remove any chemicalcomponents (e.g., CO₂, H₂S, H₂O, N₂, NH₃, H₂, CO, O₂, VOCs, and/orsiloxanes). Partially purified biogas refers to biogas that has beentreated to remove non-methane components (e.g., CO₂, H₂S, H₂O, N₃, H₂,CO, O₂, VOCs, and/or siloxanes), and requires further purification inorder to meet pipeline specifications (e.g., it may contain one or morenon-methane components in an amount that causes it to fall short ofmeeting natural gas pipeline standards or specifications). The term“biogas”, as used herein, encompasses raw biogas and partially purifiedbiogas, but does not encompass RNG, unless specified otherwise.

Referring to FIG. 2, the steps of obtaining raw biogas 10 and partiallypurifying the raw biogas 20, collectively represented as 30, areperformed at a plurality of pre-processing sites 30 _(i), 30 _(ii), 30_(iii). The partially purified biogas obtained at each pre-processingsite is collected and/or transported via a collection system (e.g., 40_(i), 40 _(ii), and/or 40 _(iii)) to the centralized biogas upgradingfacility 50 _(i), where it is upgraded to provide RNG. Advantageously,this hub-and-spoke configuration improves efficiency.

Biogas Production

In general, the raw biogas obtained in 10 and/or at each pre-processingsite 30 _(i), 30 _(ii), 30 _(iii) can be obtained from any source thatproduces biogas (e.g., a landfill or anaerobic digester). For example,the biogas may be obtained from a landfill and/or from a biogas plantthat includes one or more anaerobic digesters. In embodiments where thebiogas is obtained from a biogas plant that includes one or moreanaerobic digesters, the digesters may be connected in series and/or inparallel, may be single-stage or multi-stage digestion systems, and/ormay be designed and/or operated in a number of configurations includingbatch or continuous, mesophilic or thermophilic temperature ranges, andlow, medium, or high rates. In addition, in embodiments where the biogasis obtained from a biogas plant that includes one or more anaerobicdigesters, the digesters may be used for manure or other farm waste, forwastewater treatment, for treating industrial waste, and/or for treatingwastewater, wastes, and/or residues from an ethanol process. In oneembodiment, the biogas is sourced from one or more anaerobic digestersat a dairy farm. In one embodiment, the biogas is sourced from one ormore anaerobic digesters at a swine farm. In one embodiment, the biogasis sourced from a landfill site. In one embodiment, the biogas issourced from a wastewater treatment plant (WWTP).

Raw biogas may, for example, have a methane (CH₄) content between about35% and 75% (e.g., average of about 60%) and a carbon dioxide (CO₂)content between about 15% and 65% (e.g., average of about 35%),depending on the source. For example, without being limiting, biogasplants based on anaerobic digesters fed agricultural waste may have amethane content between about 50% and 75%, whereas biogas from alandfill site may have a methane content between about 25% and 65%. Inone embodiment, the raw biogas has a methane content between about 25%and 75% and a carbon dioxide content between about 15% and 65%, and thecarbon dioxide and methane make up at least 75% of the biogas by volume.

In general, each source of biogas may produce biogas at any rate. Forexample, one source of biogas may be a landfill that generates biogas ata rate between 3000 and 6000 SCFM (standard cubic feet per minute),whereas another source of biogas may be an anaerobic digestion (AD)facility that produces less than 1000 SCFM of biogas. In one embodimentthe biogas source (e.g., based on landfill or anaerobic digester)produces raw biogas at a rate less than 6000 SCFM (standard cubic feetper minute). In one embodiment the biogas source produces raw biogas ata rate less than 5000 SCFM. In one embodiment the biogas source producesraw biogas at a rate between 100 and 3000 SCFM. In one embodiment thebiogas source produces raw biogas at a rate between 1000 and 3000 SCFM.In one embodiment the biogas source produces raw biogas at a ratebetween 1500 and 3000 SCFM.

The percentages used to quantify gas composition and/or a specific gascontent, as used herein, are expressed as mol %, unless otherwisespecified.

Partial Purification

In general, the partial purification in 20 and/or at each pre-processingsite 30 _(i), 30 _(ii), 30 _(iii) will remove H₂O, H₂S, and/or CO₂ fromthe raw biogas to provide partially purified biogas having an H₂Ocontent, H₂S content, and/or CO₂ content that is less than that of theraw biogas. Optionally, one or more other non-methane components areremoved.

In general, the partial purification provided in 20 and/or at eachpre-processing site 30 _(i), 30 _(ii), 30 _(iii) does not produce a gasthat meets applicable quality specifications for injection into thenatural gas distribution system (e.g., pipeline standards) and/or issuitable for use in the transportation sector, but rather, requiresfurther purification (e.g., in order to qualify as RNG under applicableregulations). For example, in one embodiment, the partially purifiedbiogas has a non-methane content that is at least 20%. In oneembodiment, the partially purified biogas has a non-methane content thatis at least 15%. In one embodiment, the partially purified biogas has anon-methane content that is at least 10%. In one embodiment, thepartially purified biogas has a non-methane content that is at least 8%.In one embodiment, the partially purified biogas has an inert content(e.g., CO₂, N₂, helium, argon, neon) that is greater than 10%.

In one embodiment, the partially purified biogas has a CO₂ content lessthan 10%, less than 9%, less than 8%, less than 7%, less than 6%, orless than 5%. In one embodiment, the partially purified biogas has a CO₂content between about 4% and 8%, between about 4% and 9%, or betweenabout 4% and 10%. In one embodiment, the partially purified biogas has aCH₄ content between about 50% and about 93%. In one embodiment, thepartially purified biogas has a CH₄ content between about 50% and about90% and a N₂ content between about 10% and 20%. In one embodiment, thepartially purified biogas has a CH₄ content between about 80% and about90% and an N₂ content between about 10% and 20%. In one embodiment, thepartially purified biogas has a CH₄ content between about 72% and about90%, a CO₂ content between about 0 and 8%, and an N2 content betweenabout 5% and 20%. In one embodiment, the partially purified biogas has acombined CH₄ and N₂ content that is greater than 98%, where the N₂content is at least 5%. In one embodiment, the partially purified biogashas a combined CH₄ and N₂ content that is greater than 98%, and a CO₂content that is less than 1%. In one embodiment, the partially purifiedbiogas has a combined CH₄ and N₂ content that is greater than 98%, wherethe N₂ content is at least 5%, and wherein the CO₂ content is less than200, 100, 50, or 30 ppm.

In one embodiment, the partial purification of the raw biogas isprovided near the source of raw biogas (e.g., at a pre-processing site).For example, in one embodiment a pre-processing site is fed raw biogasdirectly from a biogas source and/or is located at a biogas plant orlandfill. In one embodiment, the pre-processing site is fed raw biogasfrom a biogas pipeline fed from one or more biogas sources. The term“pipeline”, as used herein, refers to a single pipe or an interconnectednetwork of pipes (e.g., physically connected), including any associatedpumps and valves.

In one embodiment, the partial purification of the raw biogas isprovided using a stationary purification system (e.g., installed at thepre-processing site). Using a stationary purification systemadvantageously allows the partial purification system to be readilyavailable on-site to at least partially purify the raw biogas as it isproduced. Moreover, since the purification system is stationary it canbe designed and/or selected in dependence upon the average compositionthe raw biogas from that particular source. Furthermore, since thepurification system remains on-site (e.g., is not transported with thevessels) more partially purified biogas may be transported. For purposesherein, the term “stationary” as used with reference to a purificationsystem, refers to the purification system not moving from thepre-processing site or facility at which it is used (although it maymove within the pre-processing site or facility).

In one embodiment, at least part of the partial purification is achievedusing a stationary purification system based on any suitablemethod/technology, or combination of methods/technologies, in one ormore stages, as known in the art. For example, H₂O may be removed usinga standard biogas dehumidifier, whereas H₂S may be removed using acommercial H₂S removal unit (e.g., based on activated carbon, molecularsieve, iron sponge, water scrubbing, NaOH washing, and/or biofilter orbiotrickling filter technologies). Some H₂S may also be removed duringthe water removal step, if present. O₂ may be removed by catalyticoxidation, membranes, or low pressure PSA. CO₂ may be removed byabsorption (e.g., water scrubbing, organic physical scrubbing, chemicalscrubbing), pressure swing adsorption (PSA), membrane permeation, and/orcryogenic upgrading. In one embodiment, the partial purification systemincludes a dehumidifier, a scrubber, a membrane unit, a solventextraction unit, a pressure swing adsorption unit, and/or a cryogenicunit.

In one embodiment, the partial purification is essentially a cleaning orpre-cleaning stage that does not significantly remove CO₂ or N₂. Forexample, in one embodiment, the partial purification removes H₂O and/orH₂S, but does not significantly remove CO₂ or N₂.

In one embodiment, the partial purification removes H₂O. Raw biogas maybe fully saturated with water vapour and/or may have a water content ofabout 7% (at 40° C.). Removing H₂O is advantageous since moisture cancondense into water or ice when passing from high to low pressuresystems, which may cause corrosion, may result in clogging, and/or mayinterfere with gas flow and pressure measurements (e.g., causing systemcontrol problems). In addition, the presence of water may cause hydratesto form. In one embodiment, the partial purification removes more than90%, 92%, 94%, 96%, or 98% of the H₂O present in the raw biogas. In oneembodiment, the partial purification removes more than 99% of the H₂Opresent in the raw biogas. In one embodiment, the partial purificationremoves sufficient H₂O from the raw biogas that the H₂O content ofpartially purified biogas more than meets the H₂O content specificationsfor RNG. In one embodiment, the partial purification 20 does not removeH₂O. In one embodiment, the partial purification 20 removes sufficientmoisture to provide the partially purified biogas with a H₂Oconcentration less than 0.4 g/m³ of biogas. In one embodiment, thepartial purification 20 removes sufficient moisture to provide thepartially purified biogas with a H₂O concentration less than 0.2 g/m³ ofbiogas. In one embodiment, the partial purification includes a H₂Oremoval stage that uses refrigeration techniques or desiccant drying. Inone embodiment, the partial purification includes multi-stages of H₂Oremoval (e.g., first stage of H₂O removal followed by a second stage ofH₂O removal), which may or may not be consecutive.

In one embodiment, the partial purification removes H₂S. Raw biogas mayhave an H₂S concentration between about 0 and about 6700 ppm(v) (e.g.,0-10,000 mg/m³). For example, without being limiting, biogas derivedfrom agricultural waste may have an H₂S concentration between 0-4000ppm(v), whereas biogas from a landfill may have an H₂S concentrationbetween 0 and 1000 ppm(v). H₂S is both poisonous and corrosive, and candamage piping, equipment, and instrumentation. H₂S can be reactive withmany metals, and the reactivity can be higher at higher concentrationand pressure, and/or in the presence of water. In one embodiment, thepartial purification removes more than 90%, 92%, 94%, 96%, or 98% of theH₂S present in the raw biogas. In one embodiment, the partialpurification removes more than 99% of the H₂S present in the raw biogas.In one embodiment, the partial purification removes sufficient H₂S fromthe raw biogas that the H₂S content of partially purified biogas morethan meets the H₂S content specifications for RNG. In one embodiment,the partial purification removes sufficient H₂S from the raw biogas thatthe H₂S content of partially purified biogas is safer to transport butrequires additional H₂S removal to meet RNG standards. In oneembodiment, the partial purification 20 does not remove H₂S. In oneembodiment, the partial purification removes sufficient H₂S from the rawbiogas that the H₂S concentration of partially purified biogas is lessthan 200 ppm(v). In one embodiment, the partial purification removessufficient H₂S from the raw biogas that the H₂S concentration ofpartially purified biogas is less than 100 ppm(v). In one embodiment,the partial purification removes sufficient H₂S from the raw biogas thatthe H₂S concentration of partially purified biogas is between 20 ppm(v)and 50 ppm(v). In one embodiment, the partial purification removessufficient H₂S from the raw biogas that the H₂S concentration ofpartially purified biogas is less than 50, 40, 30, 20, or 10 ppm(v). Inone embodiment, the partial purification removes sufficient H₂S from theraw biogas that the H₂S concentration of partially purified biogas isless than about 6 ppm(v). In one embodiment, the partial purificationincludes a first stage of H₂S removal (e.g., biological) followed bysecond stage of H₂S removal (e.g., an adsorption bed), which may or maynot be consecutive.

In one embodiment, the partial purification removes H₂O and H₂S.Contaminants such as O₂, NH₃, VOCs, siloxanes, and/or particulates areoptionally removed, although this is not necessary. Although the biogasupgrading system used in 50 may include H₂O and/or H₂S removal, it canbe advantageous to remove H₂O and/or H₂S prior to collection and/ortransport. For example, transporting gas with H₂S creates the risk thatin the event of a leak or accident, H₂S leaks out, thereby creatingtoxic gas and safety issues. This risk is eliminated or reduced when thepartial purification includes H₂S removal. In addition, since H₂S, andin particular the combination of H₂O and H₂S, can cause corrosionproblems, removing the H₂O and/or H₂S can reduce equipment maintenancecosts, and provide flexibility on construction materials for mobilestorage tanks. Furthermore, removing H₂S may improve the CO₂/CH₄separation if present during the partial purification.

In one embodiment, the partial purification 20 removes O₂. Removing O₂may be particularly advantageous prior to compression and transport.

In one embodiment, the partial purification 20 removes CO₂. In oneembodiment, the partial purification removes CO₂ and/or N₂. Contaminantssuch as H₂O, H₂S, O₂, NH₃, VOCs, siloxanes, and/or particulates areoptionally removed. For example, some CO₂ removal technologies alsoremove H₂S. Although the biogas upgrading system used in 50 willtypically include CO₂ and/or N₂ removal, it can be advantageous toremove CO₂ prior to collecting and/or transporting the partiallypurified biogas. Even removing half of the CO₂ present in biogas cansignificantly reduce the amount of gas that needs to be compressedand/or transported.

With specific regard to the advantages of CO₂ removal, consider thefollowing. For every quantity of biogas compressed and transported, acertain amount of equipment and energy is required. This equipmentand/or energy are associated with additional cost and greenhouse gas(GHG) emissions. Since raw biogas can contain about 60% CO₂, removingCO₂ from raw biogas can significantly reduce the amount of gasprocessed, and thus reduce the compression and/or transportation costper unit of energy delivered (i.e., which is related to the amount ofmethane). For example, removing a significant quantity of CO₂ candecrease the number of trucks and/or runs required. Accordingly,transporting partially purified biogas, particularly when CO₂ has beenremoved, is generally more efficient (e.g., in terms of both costs andGHG emission reductions) than transporting raw biogas.

In addition, the CO₂ in raw biogas can make it more challenging (e.g.,there can be phase change issues when CO₂ is compressed ordepressurized) and/or less energy efficient to compress relative to pureCH₄. Accordingly, removing even a portion of the CO₂ from raw biogas canimprove compression and/or transport to the centralized biogas upgradingfacility, by simplifying compressing and reducing compressions costs(e.g., relative to compressing raw biogas).

In one embodiment, the partial purification removes more than 90%, 92%,94%, 96%, or 98% of the CO₂ present in the raw biogas. In oneembodiment, the partial purification removes more than 20%, 30%, 40% or50% of the CO₂ present in the raw biogas. In one embodiment, the partialpurification removes between about 5% and 20% of the CO₂ present in theraw biogas. In one embodiment, the partial purification removes lessthan 5% of the CO₂ present in the raw biogas. In one embodiment, thepartial purification does not substantially remove CO₂.

In one embodiment, the partial purification removes sufficient CO₂ toincrease the heating value of the biogas by at least 50 BTU/scf, atleast 100 BTU/scf, at least 150 BTU/scf, at least 200 BTU/scf, or atleast 250 BTU/scf. For example, in one embodiment, the partialpurification increases the heating value of the biogas (e.g., which maybe about 350-500 BTU/scf) to at least 600 BTU/scf, at least 700 BTU/scf,or at least 800 BTU/scf, but retains sufficient CO₂ and/or N₂ such thatthe heating value does not exceed 900 BTU/scf, 925 BTU/scf, or 950BTU/scf. The term “heating value”, as used herein, refers to the higherheating value (HHV), unless otherwise specified.

In one embodiment, the partial purification removes sufficient CO₂ fromthe raw biogas such that the CO₂ content of partially purified biogas isless than 25%. In one embodiment, the partial purification removessufficient CO₂ from the raw biogas such that the CO₂ content ofpartially purified biogas is less than 20%, 15%, 10%, or 8%. In oneembodiment, the partial purification removes sufficient CO₂ from the rawbiogas such that the CO₂ content of partially purified biogas is lessthan 5%. In one embodiment, the partial purification removes sufficientCO₂ from the raw biogas such that the CO₂ content of partially purifiedbiogas is less than 4%.

In one embodiment, between 10% and 85% of the CO₂ is removed. In oneembodiment, between 20% and 80% of the CO₂ is removed. In oneembodiment, between 40% and 60% of the CO₂ is removed. In oneembodiment, between 84% and 90% of the CO₂ is removed. In oneembodiment, the partial purification system used removes more than 10%and less than 95% of the CO₂ in the biogas. For example, removing 10% ofthe CO₂ from a biogas containing 50% CH₄, 38% CO₂, 10% N₂, and 2% O₂,provides a partially purified biogas containing 52% CH₄, 35.6% CO₂,10.4% N₂, and 2.1% O₂, whereas removing 85% of the CO₂ from the biogascontaining 50% CH₄, 38% CO₂, 10% N₂, and 2% O₂, provides a partiallypurified biogas containing 73.9% CH₄, 8.4% CO₂, 14.8% N₂, and 3% O₂.Removing only enough CO₂ to yield a partially purified biogas having aCH₄ content that is less than 85% is advantageous in that such upgradingis relatively easy and/or can be achieved using commercial systems thatare less costly. In one embodiment, sufficient CO₂ is removed so as toprovide the partially purified biogas with a CH₄ content that is atleast 70% and no more than 90%, which may provide a good balance betweenupgrading cost and compressibility.

In this embodiment, the relative high pressures required for transportare used to improve the partial purification. In one embodiment, thepartial purification includes a water based removal of CO₂.

Although it can be advantageous to remove CO₂, H₂O, and/or H₂S from rawbiogas prior to collection and/or transport, doing so has the potentialto increase capital investment and/or operating costs (e.g., for thebiogas producer or another party), while potentially introducing aredundant step. Nevertheless, this approach offers some unique benefits.

One advantage is that since the partial purification can yield apartially purified biogas having a non-methane content that is greaterthan 10%, while still being effective for its purpose, a relativelysimple and/or inexpensive partial purification module or system can beused. Such systems may have a relatively low capital investment,operating costs, associated maintenance, space requirements, and/orappear more user-friendly. For example, a water scrubber system or arelatively simple membrane system (e.g., single stage and/or lowpermaselectivity for CO₂/CH₄ separations) are relatively affordable forsmall scale use, and are particularly suitable for partial purificationof raw biogas prior to transport to a centralized biogas upgradingfacility. Accordingly, the purification of the biogas may be conductedinto two stages. The first stage, which provides a crude purification,is provided using relatively simple and/or inexpensive equipment. Thesecond stage, which provides a more rigorous purification and is morechallenging technically, can be conducted at the biogas upgradingfacility. In this case, the more difficult second stage of purificationstill benefits from the economies of scale.

In addition, although providing partial purification prior to collectionand transport increases capital investment costs (by forsaking theeconomies of scale of centralized processing for a portion of thepurification, with multiple smaller partial purification systems insteadof a centralized facility), the aggregate cost of transporting can bereduced by permitting lower cost materials of construction or byreducing the bulk quantity that needs to be transported.

Another advantage is that since the partial purification can focus onremoving fewer components (e.g., H₂O, H₂S, and/or CO₂). these componentsmay be removed using a stationary system that can remove them moreefficiently and/or cost effectively than a mobile biogas upgrading orpurification system. For example, removing H₂S at the pre-processingsite with a dedicated H₂S removal system can be advantageouslyefficient. Moreover, it facilitates transport of the biogas at H₂Slevels that meet transportation standards.

Another advantage is that with some types of biogas upgradingtechnologies, such as simple membrane systems, there typically is atrade-off between the recovery of a component and its purity. Forexample, when using a simple membrane system to separate CH₄ and CO₂,high CH₄ yields are typically associated with a relatively large CO₂content. Alternatively, if relatively pure CH₄ is to be recovered (e.g.,with little CO₂), the CH₄ yield will be lower since some of the CH₄ willbe lost in the off-gas with the CO₂. In conventional biogas upgrading,the goal is to obtain relatively pure CH₄, and thus a significant amountof the CH₄ can be lost as methane “slip”. However, when providingpartial purification prior to transport to a centralized biogasupgrading facility, the goal can be to maximize the amount of CH₄transported to the centralized biogas upgrading facility, while removingonly some of the CO₂. Accordingly, in this configuration, the trade-offis an advantage and/or facilitates the use of less expensive equipment.

Yet another advantage is that providing partial purification at or nearthe source of raw biogas (e.g., a biogas plant) can provide additionalvalue-added products and/or facilitate recycling of the removedcomponents. For example, if water is removed, it can be recycled withinthe biogas plant. In embodiments where the partial purification includesremoving CO₂, the removed CO₂ can be recycled within the biogas plant(e.g., injected into an anaerobic digester, fed to a greenhouse, etc.)or can be provided as a value added product.

Notably, in types of biogas upgrading technologies where there is atrade-off between the recovery of a component and its purity, such assimple membrane systems, when the purity of the product (e.g., CH₄) islow, the purity of the removed product (e.g., CO₂) is often high.Accordingly, the off-gas of the partial purification system may besufficiently clean for direct discharge to the atmosphere (e.g., the CO₂removed from the raw biogas is biogenic). Another advantage is that,with some types of biogas upgrading technologies, such as membranesystems, some methane may be lost in an off-gas (e.g., methane slip). Inthis case, the methane in the off-gas can be combusted to provide energyfor the compression.

In one embodiment, the partially purified biogas is stored prior tocollection and transport (e.g., at the pre-processing site). Thepartially purified biogas can be stored using any suitable storagesystem (e.g., including any vessel). For example, the partially purifiedbiogas can be stored in a storage system that includes permanent storagetanks and/or mobile storage tanks.

In one embodiment, the partially purified biogas is stored in one ormore mobile storage tanks (e.g., a batch container that can contain gasand that can be moved from one location to another). For example, in oneembodiment, the partially purified biogas is fed into one or morecylinders mounted to or within a trailer, skid, or shipping containerthat is attachable and detachable from a truck (e.g., a tractor unit).Some examples of systems that include one or more mobile storage tanksare tube trailers and cylinder trailers.

In one embodiment, the partially purified biogas is fed in one or moremobile storage tanks as it is produced (e.g., as the partially purifiedbiogas is produced, it is fed to the one or more mobile storage tankswhere it accumulates). The one or more mobile storage tanks may bearranged to fill in tandem or parallel. For example, in one embodiment,partially purified biogas is fed to a single trailer until the traileris at capacity before the partially purified biogas is fed to anothertrailer. In one embodiment, partially purified biogas is simultaneouslyfed to a plurality of trailers. Feeding the partially purified biogas toa plurality of trailers is advantageous in that the fill rate may belower. A lower fill rate may allow more time for the heat generated fromthe compression to dissipate and/or may increase the duration betweencollection times.

In one embodiment, the partially purified biogas is compressed beforebeing fed into one or more mobile storage tanks (e.g., each mobilestorage tank may include one or more pressure vessels). In thisembodiment, the pre-processing site may include one or more compressors(e.g., where each compressor may be a multistage compressor). In oneembodiment, the pre-processing site includes a standard CNG compressor.In one embodiment, the pre-processing site includes a 3-stagenon-lubricated compressor configured to compress partially purifiedbiogas prior to being fed to the one or more mobile storage tanks.

In many instances, the raw biogas obtained in 10 will be obtained atpressures less than 10 psi (e.g., 2-3 psi). Depending on the systemand/or technology used for the partial purification, the pressure of thepartially purified biogas produced in 20 may be at a higher pressure(e.g., about 200 psig for a membrane separation). It can be particularlyadvantageous to compress the partially purified biogas to pressuresabove 1500 psig for storage in a mobile storage tank, as many trailersare designed to transport high-pressure gas (e.g., about 2000-3600psig), and thus this increases the amount of methane per tank. In oneembodiment, the partially purified biogas is compressed to above 1000psig. In one embodiment, the partially purified biogas is compressed toabove 1500 psig. In one embodiment, the partially purified biogas iscompressed to above 2000 psig. In one embodiment, the partially purifiedbiogas is compressed to between 2000 psig and 4500 psig. In oneembodiment, the partially purified biogas is compressed to between 2400psig and 4000 psig. In one embodiment, the partially purified biogas iscompressed to between 2800 psi and 4200 psig. In one embodiment, thepartially purified biogas is compressed to between 3400 psig and 3600psig. In one embodiment, the partially purified biogas is compressed toabout 3500 psig. In one embodiment, the partially purified biogas iscompressed to about 3000 psig.

Filling one or more mobile storage tanks with compressed partiallypurified biogas as the partially purified biogas is produced isadvantageous in that it may obviate the need for buffer storage, mayobviate transferring the biogas gas between storage tanks (e.g., whichmay involve compression and/or decompression), and will generally bemore efficient in terms of collecting the partially purified biogas fortransport back to the centralized biogas upgrading facility. Forexample, once a mobile storage tank is at the desired fill level (e.g.,at capacity), the entire tank can be collected (e.g., picked-up) and/ortransported to the centralized biogas upgrading facility. For example,if the mobile storage tank is part of a truck, the truck may be directedto the centralized biogas upgrading facility. If the mobile storage tankis mounted to or mounted within a skid, trailer or shipping container,the skid, trailer or shipping container may be loaded directly onto orotherwise coupled to the mode of transportation (e.g., a vehicle such asa truck, ship, rail car) for transport to the centralized biogasupgrading facility. For example, a tube trailer can be temporarilyparked at the pre-processing site until it is filled and/or collectionis arranged, at which point it is detachably coupled to the trucktractor, and transported to the centralized biogas upgrading facility.

In one embodiment, compressed partially purified biogas is fed into oneor more trailers (i.e., having mobile storage tanks) that aretemporarily parked at the pre-processing site. Once the trailers arefilled to the desired level, which may for example take between 1.5 and3 hours, they may be coupled to a truck (e.g., the same truck ordifferent trucks) and transported to the centralized biogas upgradingfacility.

In one embodiment, compressed partially purified biogas is fed into oneor more trucks (i.e., having mobile storage tanks) that are temporarilyparked at the pre-processing site. Once the trucks are filledsubstantially to full capacity or otherwise to the desired level, whichmay, for example, take several hours (e.g., about 1.5 to about 3 hours),they may be transported directly to the centralized biogas upgradingfacility. Optionally, the mobile storage tanks are removably connectedto the trucks.

Transporting the Partially Purified Biogas

In general, the partially purified biogas may be collected (e.g.,picked-up) and transported (e.g., to the centralized biogas upgradingfacility). In one embodiment, the collection of partially purifiedbiogas includes transporting the partially purified biogas at least somedistance by truck, rail, or ship. In one embodiment, the transportincludes moving a vessel containing the partially purified biogas bytruck, rail, and/or ship at least one mile. In one embodiment, thetransport includes a combination of transporting the partially purifiedbiogas in a vessel and transporting the partially purified biogas viapipeline. Transporting the partially purified biogas as a compressed gas(e.g., at 3600 psi) is advantageous in that it increases the amount ofmethane delivered per tank.

In one embodiment, where the partially purified biogas is fed in one ormore mobile storage tanks at the pre-processing site, once the mobilestorage tanks(s) have reached a certain fill level (e.g., based onpressure or density), or a pick-up is arranged, the mobile storage tanksare transported via a truck, rail, and/or ship. For example, in oneembodiment, the one or more mobile storage tanks are mounted in ashipping container that can be loaded onto a truck bed or trailer bedfor transport. In one embodiment, the one or more mobile storage tanksare mounted to a trailer that can be coupled to a truck (e.g., a towingtruck, a tractor unit, a leading trailer, or some prime moving vehicle)for transport.

In one embodiment, a trailer including one or more mobile storage tankscontaining high pressure (e.g., 3000 psi) partially purified biogas iscollected from the pre-processing site, and is then transported to thecentralized biogas upgrading facility. A trailer containing one or moreempty mobile storage tanks (e.g., under 200 psi) is then transportedback to the pre-processing site, or another pre-processing site, forexchange with a trailer containing one or more mobile storage tankscontaining high pressure, partially purified biogas.

In one embodiment, a single truck is provided to transport mobilestorage tanks containing partially purified biogas directly to thebiogas upgrading facility (e.g., direct route). In one embodiment, aplurality of trucks is provided to transport mobile storage tankscontaining partially purified biogas directly to the biogas upgradingfacility (e.g., direct route). In one embodiment, a plurality of trucks(e.g., tractor units) are provided to transport trailers or shippingcontainers containing the partially purified biogas between a pluralityof pre-processing sites and the biogas upgrading facility. In oneembodiment, a plurality of trailers containing partially purified biogasis transported by one truck (i.e., a double or triple trailerconfiguration). In one embodiment, the trucks are fueled by compressednatural gas (CNG). In general, the number of mobile storage tanks (e.g.,trailers) temporarily associated with a pre-preprocessing site willdepend on the production rate of raw biogas and/or the distance of thepre-processing site from the biogas upgrading facility.

Collecting or arranging for the collection of partially purified biogasfrom one or more pre-processing sites advantageously can exploit the useof stationary partial purification units and mobile storage tanks.Accordingly, the process/system is more efficient. For example, sincethe partially purified biogas is produced by a stationary partialpurification unit, collection (e.g., pick-up) of the partially purifiedbiogas can be more expedient as most or all of the partially purifiedbiogas can be produced before the pick-up. Even in embodiments where thepartially purified biogas is generated during pick-up, the use of thestationary partial purification unit is advantageous. For example, theuse of a stationary partial purification unit can allow the raw biogasto be at least partially purified using a unit customized for thequantity and quality of raw biogas provided at the correspondingpre-processing site. Moreover, it can efficiently remove toxic gasesfrom the raw biogas (e.g., H₂S) so that the biogas collection systemdoes not have to address transportation concerns related to the same.

Once transported, the partially purified biogas can be decompressed andremoved from the mobile storage tank(s). For example, in one embodiment,a centralized decompression unit is provided on a manifold that receivespartially purified biogas from different mobile storage tanks.Advantageously, transporting the partially purified biogas in mobilestorage tanks may obviate the need for dedicated buffer storage at thebiogas upgrading facility. For example, since the partially purifiedbiogas is transported in mobile storage tanks, the partially purifiedbiogas can be stored therein until required. Moreover, since thepartially purified biogas may be transported at high pressure, thishigher pressure may be exploited during the biogas upgrading process.

In some cases, challenges may arise when the partially purified biogascontains a significant amount of CO₂ and/or is stored at high pressure.For example, there may be issues with freezing of the lines as CO₂ gascould form dry ice upon depressurization. In one embodiment, problemsassociated with CO₂ freezing are minimized or avoided by using the heatgenerated during compression for filling the mobile pressure tank tomaintain the partially stored biogas at an increased temperature sothat, upon expansion, it does not freeze. Advantageously, this alsoreduces the amount of energy required to cool the gas after it iscompressed. In another embodiment, problems associated with CO₂ freezingare addressed by heating the compressed gas before it is depressurized(e.g., at the receiving end). Advantageously, this allows more partiallypurified biogas to be stored. In another embodiment, problems associatedwith CO₂ freezing are addressed by displacing the partially purified gasby feeding an alternate fluid into the vessels that has less propensityto freeze. In one embodiment, this fluid is a cleaner gas (e.g.relatively pure methane). In one embodiment, the fluid is a liquid,which pushes the partially purified biogas out to another location. Inone embodiment, the partially purified gas is displaced using a positivedisplacement process (e.g., a piston type of mechanism).

Biogas Upgrading

In general, the partially purified biogas transported to the centralizedbiogas upgrading facility will be further purified 50 (e.g., to produceRNG) using any suitable biogas upgrading system and/or technology. TheRNG can be used as a substitute for fossil natural gas, can be injectedinto the natural gas grid, and/or can be used as a transportation fuel.

For purposes herein, the term “renewable natural gas” or “RNG” refers tobiogas that has been upgraded to meet or exceed applicable natural gaspipeline quality standards and/or specifications, meet or exceedapplicable quality specifications for vehicle use (e.g., CNGspecifications), and/or that qualifies as RNG under applicableregulations. Pipeline specifications include specifications required forthe biogas for injection into a natural gas commercial distributionsystem. Pipeline quality standards or specifications may vary by regionand/or country in terms of value and units. For example, pipelinesstandards may require a CH₄ level that is greater than 95%. In addition,or alternatively, the natural gas pipeline standards may refer to thepurity of the gas expressed as a heating value (e.g., in British ThermalUnits (BTU)/standard cubic foot). Pipeline standards may require, forexample, that the heating value of RNG be greater than about 950BTU/scf, greater than about 960 BTU/scf, or greater than about 967BTU/scf. In the United States (US), RNG and CNG standards may varyacross the country. For example, for one company, the pipelinespecifications may require a heating value between 967 and 1110 BTU/scf,a CO₂ content less than 1.25%, an O₂ content less than 0.02%, a totalinert content (e.g., CO₂, N₂, helium, argon, neon) less than 4%, a H₂Sconcentration less than 0.25 gr/100 scf of gas, and a waterconcentration less than 7 lbs/MMscf. Whereas for another company, thepipeline specifications may require a heating value greater than 970BTU/scf, a CO₂ content less than 1.4%, an O₂ concentration less than 10ppm, a N₂ content less than 1.2%, and H₂S concentration less than 1 ppm.The specifications for CNG for vehicle use may include a heating valuebetween 940-1100 BTU/scf, a CO₂+N₂ content less than about 4%, an O₂content less than 1%, and a H₂S content less than 6 ppm(v). In oneembodiment, the RNG produced has a methane content greater than 95%. Inone embodiment, the RNG produced has a heating value greater than 950BTU/scf.

In general, the further purification provided in 50 will remove CO₂, N₂,H₂O, H₂S, O₂, NH₃, VOCs, siloxanes, and/or particulates from thepartially purified biogas to provide RNG having a CO₂, N₂, H₂O, H₂S, O₂,NH₃, VOCs, and/or siloxane content that is less than the partiallypurified biogas.

The centralized biogas upgrading facility may be an independent facilityor may be integrated with a biogas production plant. For example, in oneembodiment, the centralized biogas upgrading facility is located at ornear a landfill site. Advantageously, this configuration can providehigher quality RNG at a reduced capital cost (e.g., relative to aplurality of biogas upgrading facilities). Moreover, since there arehigher volumes fed into the centralized biogas upgrading facility (e.g.,it receives raw biogas and/or partially purified biogas from a pluralityof sources), the biogas upgrading benefits from the economies of scale(e.g., the capital cost of biogas upgrading systems are subject toeconomies of scale, where smaller plants are less capital efficient thanlarger plants).

In one embodiment, the centralized biogas upgrading facility receivesbiogas (e.g., raw and/or partially purified) at a rate greater than 4000SCFM (standard cubic feet per minute). In one embodiment the centralizedbiogas upgrading facility receives biogas at a rate greater than 6,000SCFM. In one embodiment the centralized biogas upgrading facilityreceives biogas at a rate greater than 8,000 SCFM. In one embodiment thecentralized biogas upgrading facility receives biogas at a rate greaterthan 10,000 SCFM. In one embodiment the centralized biogas upgradingfacility receives biogas at a rate greater than 15,000 SCFM. In oneembodiment the centralized biogas upgrading facility receives biogas ata rate between 10,000 and 20,000 SCFM.

In one embodiment, the centralized biogas upgrading facility is astand-alone facility located near a natural gas pipeline, and receivespartially purified biogas transported from one or more biogas sources(e.g., landfill or anaerobic digester).

The centralized biogas upgrading facility may provide one or more unitsand/or stages that remove CO₂, N₂, H₂O, O₂, NH₃, VOCs, siloxanes, and/orparticulates. These non-methane components may be removed by anycombination of chemical and/or physical technologies, in one or morestages. For example, one stage may remove more than one non-methanecomponent. The removal of H₂O, H₂S, O₂, NH₃, VOCs, siloxanes, and/orparticulates may be referred to as biogas cleaning.

Water (H₂O) may be removed from the biogas by cooling, compression,absorption. adsorption, and/or coalescing filtration. For example, watermay be removed by increasing the pressure or decreasing the temperaturein order to cause the water to condense so that it may be removed.Alternatively, water may be removed by adsorption using silicon dioxide(SiO₂), activated carbon, or molecular sieves (e.g., pressure swingadsorption).

Hydrogen sulfide (H₂S) may be removed from the biogas by adsorption onactivated carbon (e.g., impregnated activated carbon such as ZnOimpregnated carbon), adsorption on molecular sieve, adsorption usingiron oxides (e.g., iron oxide impregnated wood chips (iron sponge)),iron oxide pellets, or proprietary iron-oxide media, physical absorption(e.g., water scrubbing), chemical absorption (e.g., NaOH washing),and/or biofilters or biotrickling filters (e.g., where the biogas isforced through a moist, packed bed that contains microorganisms). SomeH₂S may also be removed during the water removal step, if present.

Siloxanes may be removed from the biogas by filtration (e.g., activatedalumina, activated carbon, graphite filtration, or silica gels, whichabsorb siloxanes from biogas), by condensation or cryogenic techniques,using synthetic resins, using liquid absorbents (e.g., Selexol™), usingmembranes, and/or using biological processes.

Particulates (e.g., dust and/or dirt) may be removed by mechanicalfilters, centrifugal separation, screens, etc. In one embodiment,particulates are removed by a coarse particulate filter (e.g., 25microns).

Nitrogen (N₂) may be removed from the biogas by pressure swingabsorption (PSA), membranes, and/or cryogenic systems. Oxygen (O₂) maybe removed by catalytic oxidation, membranes, or low pressure PSA. WhileN₂ and O₂ are not typically found in high concentrations in agriculturaland/or farm based biogas, they, and in particular N₂. may be present inhigher concentrations in biogas produced at landfills. For example,biogas derived from agricultural waste may have an N₂ content between0%-1% and an O₂ content between 0 and 0.5%, whereas biogas fromlandfills may have an N₂ content between 0% and 20% and an O₂ contentbetween 0% and 5%. Carbon dioxide (CO₂) can be removed from biogas byabsorption (e.g., water scrubbing, organic physical scrubbing, chemicalscrubbing), PSA, membrane permeation, and/or cryogenic upgrading. Forexample, in one embodiment, the biogas upgrading system includes adehumidifier, a scrubber, a membrane unit, a solvent extraction unit, apressure swing adsorption unit, and/or a cryogenic unit.

In conventional biogas upgrading, the non-methane (e.g., CO₂, H₂S, H₂O,N₂, O₂, VOCs, and/or siloxane) removal systems are selected independence upon the source of the biogas, the non-methane componentspresent, the desired purity, the capacity of the system, and othercleaning systems present, as would be understood by a person skilled inthe art. For example, since each biogas source is unique, the biogasupgrading technology, configuration, and sizing of the system componentsis typically selected in dependence upon the specific situation.However, it can be challenging to determine the best gas upgradingtechnology when the carbon dioxide levels and biogas production levels(e.g., flow rates) vary with time.

With a centralized biogas upgrading system, the system advantageouslycan be designed to upgrade biogas from a number of different sources,and thus may provide a higher quality RNG and/or the flexibility toadjust to a varying biogas production (e.g., flow rates). For example,in some instances it may not be economically justifiable to provide N₂removal for a small-scale biogas upgrading system (e.g., eitherstationary or mobile). However, by collecting and transporting partiallypurified biogas to a centralized biogas upgrading facility with N₂removal, a higher CH₄ content can be achieved.

In one particularly advantageous embodiment, the partial purificationsystem used at the pre-processing site is used to remove CO₂, but littleto no N₂, while the centralized biogas upgrading facility includes N₂removal. For example, in one embodiment the partial purification uses amembrane system to separate CO₂ and CH₄, while N₂ removal is achieved atthe centralized biogas upgrading facility using a different technologyand/or type of membrane. For example, PSA technology is efficient atremoving N₂ from biogas.

In one embodiment, where the partial purification system used at thepre-processing site is used to remove CO₂, between 10% and 85% of theCO₂ is removed. In one embodiment where the partial purification systemused at the pre-processing site is used to remove CO₂, between 20% and80% of the CO₂ is removed. In one embodiment where the partialpurification system used at the pre-processing site is used to removeCO₂, between 40% and 60% of the CO₂ is removed. In one embodiment wherethe partial purification system used at the pre-processing site is usedto remove CO₂, between 84% and 90% of the CO₂ is removed. In oneembodiment, the partial purification system used at the pre-processingsite is used to remove more than 10% and less than 95% of the CO₂ in thebiogas. For example, removing 10% of the CO₂ from a biogas containing50% CH₄, 38% CO₂, 10% N₂, and 2% O₂, provides biogas containing 52% CH₄,35.6% CO₂, 10.4% N₂, and 2.1% O₂, whereas removing 85% of the CO₂ fromthe biogas containing 50% CH₄, 38% CO₂, 10% N₂, and 2% O₂, providesbiogas containing 73.9% CH₄, 8.4% CO₂, 14.8% N₂, and 3% O₂. Removingonly enough CO₂ to yield a partially purified biogas having a CH₄content that is less than 85% is advantageous in that such upgrading isrelatively easy and/or can be achieved using commercial systems that areless costly. In one embodiment, sufficient CO₂ is removed so as toprovide the partially purified biogas with a CH₄ content that is greaterthan 70% and less than 90%, which may provide a good balance betweenupgrading cost and compressibility.

Advantageously, the partially purified biogas transported to the biogasupgrading facility may be processed as an aggregate of gases. Forexample, in one embodiment, the partially purified biogas transportedfrom a first pre-processing site is combined with partially purifiedbiogas transported from a second other pre-processing site. In oneembodiment, the partially purified biogas transported from a firstpre-processing site is combined with raw biogas from another source.Treating an aggregate of gases in a biogas upgrading facility isadvantageous in that it may improve flow rates, dilute impurities,and/or otherwise average out variability.

In one embodiment, the partially purified biogas transported from afirst pre-processing site is combined with partially purified biogastransported from a second other pre-processing site within a receivingmanifold, prior to any further purification. In one embodiment, thepartially purified biogas transported from a first pre-processing siteis combined with biogas (e.g., raw or partially purified) at a laterstage within the upgrading process. For example, in one particularlyadvantageous embodiment, the partially purified biogas transported froma first pre-processing site is combined with other biogas (e.g., raw orpartially purified) at a stage in the upgrading process selected independence upon the type and level of partial purification provide atthe first pre-processing site.

In one embodiment, the partially purified biogas transported from afirst pre-processing site is combined with other biogas (e.g., raw orpartially purified) prior to any further purification of the partiallypurified biogas. In one embodiment, the partially purified biogastransported from a first pre-processing site is combined with otherbiogas (e.g., raw or partially purified) early in the biogas upgradingprocess (e.g., before or after H₂S and/or H₂O removal, but prior to CO₂removal). In one embodiment, the partially purified biogas transportedfrom a first pre-processing site is combined with other biogas (e.g.,raw or partially purified) later in the biogas upgrading process (e.g.,after CO₂ removal).

In one embodiment, the process includes: obtaining partially purifiedbiogas derived from a first biogas source; transporting a first vesselcontaining the partially purified biogas derived from the first biogassource; removing the partially purified biogas derived from the firstbiogas source from the first vessel; combining the partially purifiedbiogas derived from the first biogas source with biogas derived from asecond other biogas source, thereby providing a combined biogas;purifying the combined biogas to provide renewable natural gas; andproviding the renewable natural gas for at least one of injection into anatural gas distribution system and use as a transportation fuel. In oneembodiment, the process comprises producing the partially purifiedbiogas. In one embodiment, producing the partially purified biogascomprises removing water, hydrogen sulfide, and/or carbon dioxide fromraw biogas obtained from the first source. In one embodiment, producingthe partially purified biogas is produced by removing water, hydrogensulfide, and carbon dioxide from raw biogas obtained from the firstsource. In one embodiment, producing the partially purified biogasincludes removing between 0% and 5% of the carbon dioxide from the rawbiogas. In one embodiment, producing the partially purified biogasincludes removing between 10% and 90% of the carbon dioxide from the rawbiogas. In one embodiment, producing the partially purified biogasincludes removing more than 90% of the carbon dioxide from the rawbiogas. In one embodiment, producing the partially purified biogasderived from the first biogas source does not include nitrogen removal,and purifying the combined biogas comprises removing nitrogen. In oneembodiment, transporting the partially purified biogas derived from thefirst biogas source comprises transporting the partially purified biogasderived from the first biogas source from a first pre-processing site toa biogas upgrading facility, said first pre-processing site fed rawbiogas from the first biogas source. In one embodiment, the biogasderived from a second other biogas source comprises partially purifiedbiogas derived from the second other source. In one embodiment, themethod comprises transporting the partially purified biogas derived fromthe second other biogas source from a second other pre-processing siteto the biogas upgrading facility, said second other pre-processing sitefed raw biogas from the second other biogas source. In one embodiment,the method comprises producing the partially purified biogas derivedfrom the first biogas source with a stationary purification unit, andcomprises compressing and feeding the partially purified biogas derivedfrom the first biogas source into the first vessel as it is produced. Inone embodiment, the partially purified biogas derived from the firstbiogas source has a methane content that is greater than an averagemethane content of raw biogas from the first biogas source, and that isless than an average methane content of the renewable natural gasproduced. In one embodiment, the method comprises obtaining a fuelcredit for the renewable natural gas. In one embodiment, the processincludes identifying an entity having a renewable natural gas supplyneed for at least one of injection into a natural gas distributionsystem and use as a transportation fuel; and providing the renewablenatural gas to the entity in an amount at least partially effective tofulfill the renewable natural gas supply need.

In one embodiment, the process includes: obtaining partially purifiedbiogas from a plurality of pre-processing sites, each pre-processingsite having a source of biogas and a stationary purification system;transporting the partially purified biogas obtained from eachpre-processing site to a biogas upgrading facility, said transportingcomprising transporting a plurality of vessels, each vessel containingpartially purified biogas obtained from one of the pre-processing sites;further purifying transported partially purified biogas at the biogasupgrading facility to renewable natural gas; and providing the renewablenatural gas for at least one of injection into a distribution system anduse in transportation. In one embodiment, the partially purified biogascollected from the plurality of pre-processing sites has a non-methanecontent of at least 10%.

In one embodiment, the process includes: at a first location, installinga first biogas purification system for processing biogas from a firstbiogas source; at a second location, installing a second other biogaspurification system for processing biogas from a second other biogassource; collecting or arranging for the collection of partially purifiedbiogas produced at each of the first and second locations, saidcollecting comprising coupling a first vessel containing partiallypurified biogas derived from the first source to at least one of atruck, rail car, and ship, and transporting the first vessel containingthe partially purified biogas; removing at least one of carbon dioxideand nitrogen from the collected partially purified biogas derived fromthe first biogas source and the second other biogas source to producerenewable natural gas; and providing the renewable natural gas.

In one embodiment, the process includes: at a pre-processing site,removing at least one of water, hydrogen sulfide, and carbon dioxidefrom raw biogas provided from a first biogas source to produce partiallypurified biogas, compressing the partially purified biogas, and feedingthe compressed partially purified biogas to a vessel as it is produced;transporting the partially purified biogas to a biogas upgradingfacility, said transporting comprising moving said vessel; furtherpurifying the partially purified biogas transported to the biogasupgraded facility to produce renewable natural gas; and providing therenewable natural gas for at least one of injection into a natural gasdistribution system and use as a transportation fuel.

Providing RNG

In general, the RNG produced at the centralized biogas upgradingfacility is provided to a user and/or distribution system (e.g., the USnatural gas grid) using any suitable method. For example, in oneembodiment, the RNG is injected directly into the distribution system.In one embodiment, the RNG is transported (e.g., by truck, rail, orship) to another location where it is injected into the distributionsystem. In one embodiment, the RNG is compressed for storage and/or toprovide compressed renewable natural gas (bio-CNG). In one embodiment,the RNG is used to provide liquefied renewable natural gas (bio-LNG).Bio-CNG and/or bio-LNG can be transported to an off-grid industrial siteand/or provided to a filling station for use in transportation.

In embodiments where the RNG is injected into distribution system, theRNG is typically compressed to pipeline pressure for the injection. WhenRNG is injected into the distribution system, an equivalent amount ofgas (i.e., measured in MMBTU) can be withdrawn at a different location.Since many NG distribution systems may recognize the transfer orallocation of the environmental attributes of RNG injected into thedistribution system to gas withdrawn at a different location, thewithdrawn gas may be considered a renewable fuel. In general, thetransfer is made on a displacement basis, where transactions within thedistribution system involve a matching and balancing of inputs andoutputs. Typically the direction of the physical flow of gas is notconsidered.

In one embodiment, a fuel credit or renewable energy credit associatedwith the RNG is generated or caused to be generated. The term “cause” or“causing”, as used herein, refers to arranging or bringing about aspecific result (e.g., a withdrawal of a gas from a distributionsystem), either directly or indirectly, or playing a role in a series ofactivities through commercial arrangements such as a written agreement,verbal agreement, or contract.

The term “credit”, “renewable fuel credit”, or “fuel credit”, as usedherein, refers to any rights, credits, revenues, offsets, greenhouse gasrights, or similar rights related to carbon credits, rights to anygreenhouse gas emission reductions, carbon-related credits or equivalentarising from emission reduction trading or any quantifiable benefits(including recognition, award or allocation of credits, allowances,permits or other tangible rights), whether created from or through agovernmental authority, a private contract, or otherwise. The renewablefuel credit may be a certificate, record, serial number or guarantee, inany form, including electronic, which evidences production of a quantityof fuel meeting certain life cycle GHG emission reductions relative to abaseline (e.g., a gasoline baseline) set by a government authority.

The generation of fuel credits or renewable energy credit associatedwith the RNG may be related to the environmental attributes of the RNGand/or the corresponding life cycle GHG emissions. To determine lifecycle GHG emissions associated with a fuel, analyses are conducted tocalculate the GHG emissions related to the production and use of thefuel throughout its life cycle. Life cycle GHG emissions include theaggregate quantity of GHG emissions related to the full life cycle ofthe transportation fuel, including all stages of fuel and feedstockproduction and distribution, from feedstock generation or extraction,through the distribution and delivery, and use of the finished fuel tothe ultimate consumer. GHG emissions typically account for total net GHGemissions, both direct and indirect, associated with feedstockproduction and distribution, the fuel production, and distribution anduse.

In one embodiment, the RNG is provided for use as a transportation fueland a fuel credit is generated or caused to be generated. Providing theRNG for transportation use is advantageous because fuel credits can belucrative. Examples of fuel credits include, Renewable IdentificationNumbers (RINs) under the United States Environmental Protection Agency(EPA) Renewable Fuel Standard and carbon credits under state supportedlow carbon fuel standards within the United States (e.g., The Low CarbonFuel Standard in California).

In one embodiment, the generation of fuel credits is enabled by thetransfer or allocation of the environmental attributes of the RNGinjected into a distribution system to the natural gas withdrawn fromthe distribution system. The transfer or allocation of environmentalattributes may be evidenced by a contract or other commercialarrangement (e.g., may or may not involve transfer of ownership). Bytransferring or allocating “environmental attributes”, it is meant thatthe natural gas withdrawn from the distribution system fortransportation use is considered to have the GHG emission properties ofthe RNG injected, as can be readily determined by those of skill in theart.

In one embodiment, inputs and outputs to the natural gas distributionsystem are tracked by flow meters and/or electronic recording. In oneembodiment, inputs and outputs are traced using energy delivered. Theterm “energy delivered”, as used herein, is a measure of the amount ofenergy delivered to or from the distribution system in a particular timeperiod, or series of time periods (e.g., discrete increments of time),such as, without limitation, hourly, daily, weekly, monthly, quarterly,or yearly intervals. The energy delivered may be obtained afterdetermining values representing the energy content and volume of flowfor a particular time period. For example, the energy delivered may beprovided in units of gigajoules (GJ), million British thermal units(MMBtu), or British thermal units (Btu)) over a given time period.

In one embodiment, the natural gas withdrawn for transportation use orthe renewable natural gas produced at the upgrading facility is used asan intermediate or a feedstock to produce the transportation fuel. Forexample, the natural gas to which the environmental attributes have beentransferred may be chemically reacted to produce renewable hydrogen,which in turn is used in a process to produce a renewable liquidtransportation fuel, a partially renewable liquid transportation fuel,or a liquid transportation fuel having renewable content. In certainembodiments, the renewable hydrogen may be combined with a crude oilderived liquid hydrocarbon so that it becomes incorporated into thehydrocarbon and ultimately becomes part of the liquid transportationfuel that is the product of the fuel production facility.

In one embodiment, the RNG or natural gas withdrawn for transportationuse is used as a transportation fuel that has life cycle GHG emissionsthat are at least 20% less than the life cycle GHG emissions of agasoline baseline using EPA methodology, preferably at least 50% or 60%less.

Description of Embodiments of the Invention

FIG. 3a shows an embodiment of a system in accordance with an embodimentof the invention. The system includes a plurality of pre-processingsites 30 a _(i), 30 a _(ii), each of which includes a source of rawbiogas 10 a (e.g., feed from landfill, anaerobic digester, and/or biogaspipeline) and a partial purification system 20 a (i.e., for removingH₂O, H₂S, and/or CO₂ from the raw biogas), and optionally includes acompressor system 25 a and/or a storage system 28 a. The system alsoincludes a collection system 40 a (e.g., including one or more trucks,ships, or rail), for collecting and transporting the partially purifiedbiogas produced at each biogas pre-processing site 30 a _(i), 30 a _(ii)to a centralized biogas upgrading facility 50 a. The centralized biogasupgrading facility includes a system 60 a for providing RNG.

Advantageously, since the centralized biogas upgrading facility 50 a canreceive partially purified biogas from a plurality of pre-processingsites, it may be a relatively large scale facility and may profit fromthe economies of scale. In comparison to a small-scale biogas upgradingsystem (e.g., farm-scale or mobile), a large-scale biogas upgradingsystem (e.g., >6000 SCFM) can remove more impurities (e.g., providing amethane content of at least 98%) at a reasonable cost.

FIG. 3b shows an embodiment of a system in accordance with oneembodiment of the invention. The system includes a plurality ofpre-processing sites 30 b _(i), 30 b _(ii), each of which includes asource of raw biogas 10 b (e.g., feed from landfill, anaerobic digester,and/or biogas pipeline) and a partial purification system 20 b (i.e.,for removing H₂O and/or H₂S from the biogas), and optionally includes acompressor system 25 b and/or a storage system 28 b. The system alsoincludes a collection system 40 b (e.g., including one or more trucks,ships, or rail), for transporting the partially purified biogas producedat each site 30 b _(i), 30 b _(ii) to a centralized biogas upgradingfacility 50 b. Also included is a system for injecting the RNG into adistribution system 61 b and/or a system for transporting RNG (e.g.,compressed or liquefied) to a filling station 62 b. The RNG can be usedas a transportation fuel and fuel credits may be generated.

In this embodiment, the partial purification system 20 b at thepre-processing sites 30 b _(i) and 30 b _(ii) removes H₂O and H₂S, butdoes not significantly remove CO₂. Accordingly, the partial purificationreduces corrosion and/or other complications, but does not significantlyimprove compression. Rather, the CO₂ derived from the raw biogas isprimarily removed at the centralized biogas upgrading plant, where itmay be vented or provided as a value-added product. This configurationis particularly advantageous when the CO₂ is removed by scrubbing, assuch systems particularly benefit from the economies of scale.

FIG. 3c shows an embodiment of a system in accordance with oneembodiment of the invention. The system includes a plurality ofpre-processing sites 30 c _(i), 30 c _(ii), each of which includes asource of raw biogas 10 c (e.g., feed from landfill, anaerobic digester,and/or a biogas pipeline) and a partial purification system 20 c (i.e.,for removing H₂O, H₂S, and/or CO₂ from the raw biogas), and optionallyincludes a compressor system 25 c and/or a storage system 28 c. Thesystem also includes a collection system 40 c (e.g., including one ormore trucks, ships, or rail, and optionally including a biogaspipeline), for transporting the partially purified biogas produced ateach pre-processing site 30 c _(i), 30 c _(ii) to the centralized biogasupgrading facility 50 c. The centralized biogas upgrading facilityincludes a system for 61 c for providing RNG (e.g., compressed orliquefied). The RNG can be used for transportation and fuel creditsgenerated.

In this embodiment, the partial purification system 20 c at the firstpre-processing site 30 c _(i) removes H₂O and H₂S, and either removes noCO₂ or removes an inadequate amount of CO₂ to provide RNG (i.e., theresulting partially purified biogas must undergo further CO₂ removal toqualify as RNG). The partial purification system 20 c at the secondpre-processing site 30 c _(ii) removes most of the CO₂ in the rawbiogas, but the resulting partially purified biogas must undergo N₂removal to qualify as RNG. For example, the partial purification system20 c at 30 c _(ii) may include a membrane system or scrubbing system forremoving CO₂ with low methane loss. In this embodiment, the partiallypurified biogas transported from the first pre-processing site 30 c _(i)and the partially purified biogas transported from the secondpre-processing site 30 c _(ii) are introduced into different stages ofthe biogas upgrading process. For example, since the partially purifiedbiogas transported from the first pre-processing site 30 c ₁ has alreadybeen subject to H₂O and/or H₂S removal, but still needs the CO₂ contentto be reduced, it is introduced downstream of the H₂O and/or H₂S removalstage, but upstream of or into the CO₂ removal stage. Since thepartially purified biogas transported from the second pre-processingsite 30 c _(ii) has already been subject to adequate CO₂ removal, it isintroduced downstream of the CO₂ removal stage (e.g., upstream of orinto the N₂ removal stage).

Advantageously, this configuration enables N₂ to be removed from thebiogas obtained at pre-processing site 30 c _(ii) at relatively low cost(e.g., compared to using a small scale or mobile biogas upgradingsystem). For example, since not all biogas production plants produceenough biogas to justify investing in N₂ rejection, providing partialpurification and transport to an upgrading facility allows the partiallypurified biogas to be further polished to pipeline standards usingtechnologies and/or system not economically feasible on a small scale.

In this embodiment, the partially purified biogas transported from thefirst pre-processing site 30 c _(i) is optionally combined with biogasderived from a different source prior to or during treatment in the CO₂stage of the process. The partially purified biogas transported from thesecond pre-processing site 30 c _(ii) is optionally combined with biogasderived from the first pre-processing site 30 c _(i) and/or biogasderived from a different source prior to or during the treatment in theN₂ removal stage of the process.

In addition to removing redundant steps (e.g., the partially purifiedbiogas transported from the second pre-processing site 30 c _(ii) isonly treated to remove CO₂ once), this configuration may reducecompression costs and/or may improve the removal of CO₂. For example,consider the following. The partially purified biogas transported fromthe plurality of pre-processing sites 30 c _(i), 30 c _(ii) can be at arelatively high pressure (e.g., 2400-3600 psi) in these embodiments.Prior to being fed into the biogas upgrading system 50 c, it typicallywill be decompressed. Early stages of the biogas upgrading process maybe designed to process raw biogas at low pressure (e.g., <10 psi),whereas later stages (e.g., CO₂ removal) may benefit from higherpressures (e.g., 200 psi). By introducing the partially purified biogasinto a stage in the process that requires and/or benefits fromrelatively high pressures, the decompression required for the earlierlow pressure stage and subsequent recompression required for asubsequent high pressure stage is avoided. Moreover, since many CO₂removal technologies, such as membrane separation, may perform better athigher pressures, this configuration may improve CO₂ removal.

FIG. 3d shows an embodiment of a system in accordance with oneembodiment of the invention. The system includes one or morepre-processing sites 30 d ₁, 30 d _(ii), each of which includes a sourceof biogas 10 d (e.g., feed from landfill, anaerobic digester, and/orbiogas pipeline) and a partial purification system 20 d (i.e., forremoving H₂O, H₂S, and/or CO₂ from the raw biogas), and optionallyincludes a compressor system 25 d and/or a mobile storage system 28 d.The system also includes a collection system 40 d (e.g., including oneor more trucks, ships, or rail, and a biogas pipeline system), fortransporting the partially purified biogas produced at eachpre-processing site 30 d _(i), 30 d _(ii) directly to a centralizedbiogas upgrading facility 50 d. The centralized biogas upgradingfacility includes a system for distributing the RNG 60 d (e.g.,injection into a distribution system). Optionally, the system includes asystem for injecting compressed CO₂ into a CO₂ pipeline system 70 d.

In this embodiment, the centralized biogas upgrading facility 50 d islocated at or near, and/or is fed raw biogas directly from, a landfill11. In this case, the partially purified biogas collected from the oneor more pre-processing biogas production sites (i.e., illustrated as twosites 30 d _(i), 30 d _(ii), but could be more or less), supplements theflow of biogas to the biogas upgrading system, thereby providingflexibility to adjust to varying biogas production (e.g., flow rates),and/or profiting from the economies of scale.

In this embodiment, the partially purified biogas derived from the firstbiogas source 10 d _(i) may combined with the partially purified biogasderived from the second source 10 d _(ii) within the receiving manifoldthat feeds the biogas upgrading system 50 d, and/or can be combined withbiogas derived from the landfill site 11 at a selected stage in theprocess.

The embodiment discussed with reference to FIG. 3d is particularlyadvantageous. For example, since landfill sites can produce largequantities of biogas (e.g., 10,000 SCFM), the landfill can provide theprimary source of biogas and/or justification for the centralized biogasupgrading facility. When biogas production at the landfill wanes (e.g.,as the landfill ages), the number of and/or contribution frompre-processing sites may be increased.

In addition, these configurations may be particularly advantageousbecause, since the partially purified biogas typically will becompressed to a relatively high pressure in the mobile storage system(e.g., greater than 1000 psig), the use of a biogas purificationtechnology that uses higher pressures (e.g., greater than 200 psig,greater than 300 psig, greater than 400 psig, or greater than 400 psig),may be more attractive.

In one embodiment, the relatively high pressure of the partiallypurified biogas is exploited in the centralized biogas upgrading. Forexample, carbon dioxide may be removed from biogas using a two stagemembrane system using an inlet pressure of about 100 psig or 200 psig.However, by using a higher inlet pressure (e.g., greater than 600 psigor greater than 800 psig), a single stage membrane can be used to removeabout the same amount of carbon dioxide. While it is normallychallenging to justify the increased compression costs corresponding tohigher pressures, since the partially purified biogas may be compressedto above 1000 psig as it fills the mobile storage system, the increasedcost may be offset. In one embodiment, the partially purified biogas isfed to a membrane system at a pressure greater than 200 psig, greaterthan 300 psig, greater than 400 psig, greater than 500 psig, greaterthan 600 psig, greater than 700 psig, or greater than 800 psig.

In one embodiment, the partially purified biogas is fed to a CO₂ removalthat uses scrubbing (e.g., Selexol™ or water), which removes most of theCO₂ and preserves the pressure of the resulting gas stream.Depressurization of the resulting gas can cool that gas and/or gas fromthe landfill to create conditions for cryogenic separation of the CH₄from N₂.

In the embodiments illustrated in FIGS. 3a to 3d , the pre-processingbiogas production sites (e.g., 30 a _(i), 30 d _(i), 30 d _(ii)) have apartial purification system used for removing H₂O, H₂S, and/or CO₂ fromraw biogas (e.g., leaving a non-methane content of at least 10%).Although such systems are less costly than small-scale biogas upgradingsystems that provide pipeline quality upgraded biogas, it can still bean added expense for farmers and/or small scale landfills.

In accordance with one embodiment of the invention, another party (e.g.,separate from the biogas producer) arranges for the provision,installation, and/or operation of the partial purification system at thepre-processing biogas production site (and optionally a plurality ofother pre-processing sites), and for the collection and transport of thepartially purified biogas from each pre-processing site to thecentralized biogas upgrading system. Accordingly, there is additionalincentive for small scale biogas sources to upgrade raw biogas topipeline quality. In particular, this embodiment makes biogas upgradingaccessible to any small scale biogas source. More specifically, it opensup additional options for small biogas sources (e.g., individual farms)located far from a biogas grid.

Providing, installing, and/or operating a remote partial purificationsystem is advantageous with regard to the collection of the partiallypurified biogas. For example, it allows partially purified biogas to beproduced prior to collection thereof thereby improving the speed of thecollection. In addition, it allows the partially purified biogas to becompressed and fed directly into a mobile storage tank, which mayobviate using buffer storage and/or flaring of excess biogas, andimproves the collection by allowing the transport of relatively largebatches of partially purified biogas (e.g., in a hub-and-spokeconfiguration). For example, it is more efficient to transport one largebatch directly to the biogas upgrading facility, than to provide asuccessive collection where smaller volumes are collected at a pluralityof sites before being transported to the centralized biogas upgradingfacility.

Providing, installing, and/or operating a remote partial purificationsystem, and collecting the partially purified biogas for transport tothe centralized biogas upgrading facility is advantageous for the biogasupgrading facility in that it merits providing a larger and/or moreefficient biogas upgrading system. Economies of scale indicate thatlarger plants are favored for producing higher quality gas, lowermethane losses, higher plant efficiency, and higher profitability.

In the embodiments illustrated in FIGS. 3a to 3d , the centralizedbiogas upgrading system not only provides improved biogas upgrading, butcan also provide a centralized injection into the distribution system.This is advantageous because even if upgrading to pipeline quality iseconomically feasible for a given situation, injection into adistribution system or a commercial fuel station may not be possibleand/or may be unfavorable.

Advantageously, the embodiments described herein provide lower capitalcost per unit of RNG used for fuel credit generation, making the use ofbiogas for use in transportation economically practical. Furthermore, itallows impractically small biogas productions to be to be collected andused, which reduces overall GHG emissions. By upgrading impracticallysmall biogas productions to pipeline standards (e.g., provide RNG) fortransportation use, overall GEIG emissions are further reduced.

Of course, the above embodiments have been provided as examples only. Itwill be appreciated by those of ordinary skill in the art that variousmodifications, alternate configurations, and/or equivalents will beemployed without departing from the spirit and scope of the invention.Accordingly, the scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

1. A method for upgrading biogas comprising: (a) obtaining biogas from a plurality of biogas sources, including a first biogas from a first biogas source and a second other biogas from a second other biogas source; (b) removing one or more components from the first biogas to produce a first partially purified biogas, said one or more components comprising hydrogen sulfide, carbon dioxide, or a combination thereof, said one or more components removed using at least one stationary purification system; (c) transporting a first vessel containing the first partially purified biogas from the first biogas source directly to a biogas upgrading facility; (d) removing one or more components from the second biogas to produce a second partially purified biogas, said one or more components comprising hydrogen sulfide, carbon dioxide, or a combination thereof, said one or more components removed using at least one stationary purification system; (e) transporting a second vessel containing the second partially purified biogas from the second biogas source directly to the biogas upgrading facility; (f) at the biogas upgrading facility, removing at least one component from a gas stream comprising the first partially purified biogas, the second partially purified biogas, or a combination thereof, to produce renewable natural gas having a heating value that is greater than a heating value of any one of the first and second partially purified biogases; (g) providing the renewable natural gas produced in (f) for injection into a distribution system, for use as a transportation fuel, or for a combination thereof.
 2. The method according to claim 1, wherein the one or more components removed in step (b) comprise carbon dioxide.
 3. The method according to claim 2, wherein the at least one component removed in step (f) comprises carbon dioxide.
 4. The method according to claim 3, wherein the first partially purified biogas has a heating value of at least 750 BTU/scf and less than 925 BTU/scf.
 5. The method according to claim 2, wherein step (b) comprises removing at least 50% of the carbon dioxide in the first biogas.
 6. The method according to claim 2, wherein step (b) comprises removing at least 75% the carbon dioxide in the first biogas.
 7. The method according to claim 2, wherein step (b) comprises removing at least 85% the carbon dioxide in the first biogas.
 8. The method according to claim 2, wherein the first partially purified biogas has a carbon dioxide content that is less than 8%.
 9. The method according to claim 8, wherein the first partially purified biogas has a nitrogen content that is at least 5%, and where step (f) comprises removing nitrogen.
 10. The method according to claim 1, wherein the one or more components removed in steps (b) and (d) comprise carbon dioxide, water, and hydrogen sulfide.
 11. The method according to claim 4, wherein the one or more components removed in steps (b) and (d) comprise carbon dioxide, water, and hydrogen sulfide.
 12. The method according to claim 1, wherein the plurality of biogas sources comprises a third biogas source, where the biogas upgrading facility is connected to the third biogas source by a piping system, and wherein the third biogas source is a landfill.
 13. The method according to claim 1, wherein the first vehicle is a truck, rail car, or ship.
 14. The method according to claim 1, wherein the first vessel is transported to the biogas upgrading facility in a trailer, by truck.
 15. The method according to claim 1, wherein the first vessel is filled with the first partially purified biogas to a pressure of at least 1000 psig.
 16. The method according to claim 1, wherein step (b) comprises subjecting the first biogas from the first biogas source to a membrane separation.
 17. The method according to claim 1, wherein the first and second vessels are powered by natural gas, renewable natural gas, or a combination thereof.
 18. The method according to claim 1, wherein the plurality of biogas sources are selected to provide the biogas upgrading facility with biogas at rate of at least 2,000 SCFM.
 19. The method according to claim 1, wherein the plurality of biogas sources are selected to provide the biogas upgrading facility with biogas at rate of at least 5,000 SCFM.
 20. A method for upgrading biogas comprising: (a) obtaining biogas from a plurality of biogas sources, including a first biogas from a first biogas source and a second other biogas from a second other biogas source; (b) feeding the first biogas into a first stationary purification system to remove hydrogen sulfide, carbon dioxide, or a combination thereof from the first biogas and produce a first partially purified biogas having a heating value less than 950 BTU/scf; (c) transporting a first vessel containing the first partially purified biogas from the first biogas source directly to a biogas upgrading facility by vehicle; (d) feeding the second biogas into a second other stationary purification system to remove hydrogen sulfide, carbon dioxide, or a combination thereof from the second biogas and produce a second partially purified biogas having a heating value less than 950 BTU/scf; (e) transporting a second vessel containing the second partially purified biogas from the second biogas source directly to the biogas upgrading facility by vehicle; (f) at the biogas upgrading facility, feeding the first and second partially purified biogases into one or more purification systems to remove carbon dioxide, nitrogen, oxygen, or any combination thereof and to produce renewable natural gas having a heating value that is at least 950 BTU/scf; (g) providing renewable natural gas produced in (f) for injection into a distribution system, for use as a transportation fuel, or for a combination thereof. 21-45. (canceled) 